Question

What is the potential energy of the soap film formed on a frame of area $4\times {10}^{-3}{m}^2?$ If the area of the film is reduced by half, the change in its potential energy will be ( surface tension of the soap solution is $40\times {10}^{-5}H/m)$

• A. $32\times {10}^{-5}J,16\times {10}^{-5}J$
• B. $16\times {10}^{-5}J,8\times {10}^{-5}J$
• C. $48\times {10}^{-5}J,12\times {10}^{-5}J$
• D. $36\times {10}^{-5}J,2\times {10}^{-5}J$

Answer 1

The correct option is A $32\times {10}^{-5}J,16\times {10}^{-5}J$

Potential energy of the firm

= 2TA

$=2\times 40\times {10}^{-3}\times 4\times {10}^{-3}$

$=32\times {10}^{-5}J$

Change in potential energy

$=2T△A$

$=2\times {10}^{-3}[4\times {10}^{-3}-2\times {10}^{-3}]$

$=16\times {10}^{-5}J$